Measurement of overinflation by multiple linear regression analysis in patients with acute lung injury

Abstract

aaAcute lung injury (ALI) results in an increase in permeability, recruitment of neutrophils and impairment of the surfactant system. Although increased permeability in patients with the acute respiratory distress syndrome (ARDS) is evenly distributed across the lung [1], regional lung inflation is markedly heterogeneous [2,3]. Increased lung weight tends to collapse a dependent lung, while nondependent lung is more normally aerated. Since a relatively small lung is ventilated, excessive tidal volumes could overdistend some alveoli and produce further lung injury.In order to prevent overdistension, current recommendations target ventilatory plateau pressures <30-35 cmH 2 O [4,5], since total lung capacity is normally achieved at this level of transalveolar pressure. However, the end-inspiratory lung volume (VEI), rather than the airway pressure (Paw), appears to determine whether lung injury occurs [6]. This was confirmed in a recent clinical study where up to 90% of ARDS patients showed evidence of overinflation below a plateau pressure of 35 cmH 2 O [7].Static volume-pressure curve analysis has been used to define lung overinflation, with the upper inflection point denoting a sudden increase in elastance with further inflation. However, static techniques are not widely used. Since a prolonged pause is needed for equilibration of gas flow and respiratory muscle activity may also result in an unstable end-expiratory lung volume (EELV), the subject must be paralysed. If a super-syringe technique is used allowance must be made for the continuing gas exchange [8] and patients may develop hypoxaemia. Finally, respiratory mechanics are only described at a single point in a continually evolving process.Dynamic volume-pressure curve analysis offers online, potentially continuous, measurements that do not interfere with ventilation and produce a "functional" description of lung mechanics [9]. Dynamic data may also reflect the contribution of heterogeneous time constants to lung overinflation. At a given respiratory rate short time constant lung units will receive proportionately more ventilation than long time constant lung units, possibly contributing to regional overinflation [10]. This effect would not be detected by static volume-pressure curve analysis, but would contribute to both dynamic curve changes and possibly to ventilator-induced lung injury.Models for estimating overinflation from dynamic volume-pressure curves, by partitioning dynamic respiratory elastance (Ers,dyn) into volume-independent (E 1 ) and volume-dependent (E 2 ) components [11][12][13], have only recently been described. However, this technique has not been Measurement of overinflation by multiple linear regression analysis in patients with acute lung injury. A.D. Bersten. ERS Journals Ltd 1998.ABSTRACT: Strategies to optimize alveolar recruitment and prevent lung overinflation are central to ventilatory management of patients with acute lung injury (ALI). The recent description of overinflation using multilinear regression analysis of airway...

A minimal model of lung mechanics and model-based markers for optimizing ventilator treatment in ARDS patients

“…The model was validated by fitting to clinical PV data at different PEEP levels reported in the literature [31]. The study used data from 10 patients each with a different level of lung injury.…”

“…The model was validated by using clinical data from Bersten [31]. The results of this model show that as PEEP increases, the TOP distribution mean decreases, while the TCP distribution mean increases.…”

“…However, this measurement can be obtained by deflating the lung to atmospheric pressure. Once the airway is opened to atmospheric pressure, the lung assumes FRC rapidly, and the entire measuring process can be completed in a matter of seconds [31]. This value might have to be obtained one per every 1 -2 days.…”

Model-Based Approach to Estimate dFRC in the ICU Using Measured Lung Dynamics

“…PEEP prevents alveolar collapse and enhances gas exchange using higher pressure to recruit the collapsed alveoli. However, high PEEP and tidal volume (V t ) can also damage healthy alveoli (Bersten, 1998).…”

Dynamic functional residual capacity can be estimated using a stress–strain approach

“…PEEP can be used to increase FRC, however there is a risk of overstretching healthy lung units in the process [12].…”